The present invention relates to systems for controlling the flow of refrigerant in a refrigeration or air conditioning system of the type employing the well known mechanical thermal expansion valve. Typically, valves of this type have an auxiliary passage therethrough adapted for attachment to the discharge line of the refrigerant evaporator for receiving flow therefrom and for connection to the compressor suction return line. The auxiliary passage through the valve body provides a convenient location to sense the temperature of the evaporator discharge for purposes of providing an electric control signal which may be employed in a microcomputer for controlling the operation of the compressor clutch and condenser cooling fan.
Where it is desired to provide electrical sensing of the temperature in the auxiliary refrigerant passage in the thermostatic expansion valve, it has been found desirable to employ a thermistor in the passage for direct fluid temperature sensing. However, providing the mounting of the thermistor through the valve block from the exterior thereof and to provide adequate sealing around the thermistor for preventing leakage of the gaseous refrigerant has been troublesome in high volume mass production. Heretofore, it has been the practice to mount the thermistor on a metal flange and secure the flange to the periphery of a port formed in the valve body to access the auxiliary refrigerant passage. This technique for mounting the thermistor as a sub-assembly has been found to troublesome in high volume production of the valves where breakage of the thermistor has been experienced during the sealing operation which typically employ metal staking. Accordingly, it has been desired to provide a way or means of attaching a thermistor to a sensing port in the valve block after the port has been sealed to retain the pressurized gaseous refrigerant.
It has further been desired in providing a refrigerant temperature sensor in a thermal expansion valve passage to incorporate electronic circuitry at the thermistor location in order that the circuitry may be heat sinked to the low temperature valve block and thereby provide cooling for solid state switching devices handling substantial electrical current flow.